(a) Field of the Invention
The present invention relates to a variable valve lift apparatus. More particularly, the present invention relates to a variable valve lift apparatus that can adjust a valve lift amount in response to an operational state of an engine.
(b) Background
Generally, an automotive engine includes a combustion chamber in which fuel burns to generate power. The combustion chamber is provided with an intake valve for supplying a gas mixture containing the fuel and an exhaust valve for expelling the burned gas. These intake and exhaust valves open and close the combustion chamber by a valve lift apparatus connected to a crankshaft.
A conventional valve lift apparatus use a cam formed in a predetermined shape and provide a fixed amount of valve lift. As a result, it is impossible to adjust the amount of a gas that is being introduced or exhausted. Therefore, the engine cannot run at its optimum state for various driving ranges.
For example, if a valve lift apparatus is designed to optimally respond to a low driving speed, the time for opening valve and the amount of valve lift are not sufficient for a high speed driving state. On the contrary, when the valve lift apparatus is designed to optimally respond to a high speed driving state, an opposite phenomenon occurs in the low speed driving state.
In order to solve the above-described drawback, a variable valve lift apparatus has been researched and developed. A variety of variable lift apparatuses such as a locker arm type variable valve lift apparatus, a direct drive type variable valve lift apparatus, a swing arm type variable valve lift apparatus have been developed.
For example, a conventional high-low cam separation type variable valve lift apparatus has an excellent operational stability and a high degree of design freedom because the low and high cams are separately provided. However, such high-low cam separation type variable valve lift apparatus has a problem in that the driving mass increases and therefore it is not likely to be developed into a cutting-edge technology. In particular, the high-low cam separation type variable valve lift apparatus is not likely to be developed as a continuously variable valve lift.
A conventional swing arm type 2-stable variable valve lift has an inner body for driving a low cam and an outer body for driving a high cam. As a result, it has a drawback in that the driving mass increases and its structural rigidity is deteriorated, making it hard to be used for high speed driving.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.